1. Field of the Invention
The present invention relates to a process for making a hydroentangled cellulose product comprising cellulose fibers and to products obtainable by said process.
It is known to produce nonwoven webs by so-called “melt-blowing” processes from various synthetic polymers.
2. Description of the Related Art
It is, furthermore, known to produce nonwoven webs made by a melt-blowing process employing a cellulose solution in N-methyl-morpholine-N-oxide (“NMMO”) from, inter alia, WO 98/26122, WO 99/47733, WO 98/07911, U.S. Pat. No. 6,197,230, WO 99/64649, WO 05/106085 EP 1 358 369, WO 02/52070 and US 2005/56956. Such products are also generally mentioned in DE 101 40 772 A1 and in WO 2007/000319 A1.
The melt-blowing processes disclosed in the above-referenced documents are characterized in that extruded threads of the cellulose solution in NMMO are picked up by a gas stream flowing in a generally parallel direction to the path of the filaments. The cellulose solution, which is ejected through the orifices, is formed to liquid strands or latent filaments, which are drawn (or significantly decreased in diameter and increased in length and may be split into several sub-filaments) by the gas stream.
The filaments are then collected, for example on a rotating drum, whereby a web is formed.
In the following, this process is referred to as “Lyocell melt-blowing process”. Nonwoven melt-blown webs made by the Lyocell melt-blowing process will in the following be referred to as “Lyocell melt-blown webs”. For the purposes of the present invention, the term “Lyocell melt-blowing process” encompasses both processes by which endless filaments are obtained (such processes also referred to in the literature as “spunbonding processes”), processes by which fibres of a discrete length are obtained and processes by which mixtures of endless filaments and fibres of discrete length are obtained.
In contrast thereto, WO 06/035458 discloses a process for the production of so-called “spunlaid nonwovens”, i.e. the extruded filaments are not stretched by a gas stream, but by the flow of the precipitation fluid.
Various means of bonding nonwoven webs are known nowadays. These means, depending on the nature of the nonwoven web employed, comprise chemical bonding, thermal bonding, needle-bonding and bonding via hydroentanglement.
WO 2007/124521 (not pre-published) discloses a process wherein a Lyocell melt-blowing process is combined with a hydroentanglement step, whereby it is possible to produce bonded webs with excellent properties for a variety of end-uses, with the additional advantage of various synergistic effects.
The process for the production of a hydroentangled product comprising cellulose fibers according to WO 2007/124521 comprises the steps of
extruding a solution comprising cellulose dissolved in an aqueous tertiary amine-oxide through a spinneret into an air gap, thereby forming filaments
contacting said filaments in the air gap with a medium which at least partially coagulates the filaments
drawing said filaments by means of a gaseous stream
collecting and precipitating said filaments in order to form a web
bonding said web by means of a hydroentanglement process.
By this process, stable light weight webs resulting from the melt-blown process can be further processed into a bonded web in an especially convenient way.
According to WO 2007/124521, a Lyocell melt-blown web may be bonded using a spunlace line with 3 pressure heads, the first head operating at around 20 bars, the second head operating at the upper side at around 100 bar and the third head operating at the lower side at around 100 bar. The line speed may be around 40 m/min. If the hydroentanglement step is conducted in an overall continuous process on a never-dried Lyocell melt-blown, the production speed of the spunlace line can be adjusted according to the rate of supply of the web.